A photographic process utilizing silver halide has heretofore been most widely used since it is superior in photographic characteristics such as sensitivity and control of gradation to other photographic processes such as an electrophotographic process and a diazo photographic process. For photographic processing of light-sensitive materials using silver halide, a technique has recently been developed which enables to form images in a simplified manner and rapidly by substituting a dry processing system including a heating process for a conventional wet processing system utilizing developing solutions.
Heat developable light-sensitive materials are known in the art, and their details (including their processes of preparation) are described in, for example, Shashin Kogaku No Kiso, published by Corona Co. (1979), pages 553-555, Eizo Joho, published April 1978, page 40, Nebletts Handbook of Photography and Reprography, 7th ed., Van Nostrand Reinhold Company, pages 32-33, U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020, 3,457,075, British Pat. Nos. 1,131,108, 1,167,777, and Research Disclosure, June 1978, pages 9-15 (RD-17029).
Many processes have been proposed for the formation of color images by the dry processing system.
One of the processes is to form color images by coupling an oxidized product of a developing agent with a coupler. In connection with this process, U.S. Pat. No. 3,531,286 discloses p-phenylenediamines as reducing agents and phenolic or active methylene couplers; U.S. Pat. No. 3,761,270 discloses p-aminophenol-based reducing agents; Belgian Pat. No. 802,519 and Research Disclosure, September 1975, pages 31-32 disclose sulfonamide-based reducing agents; and U.S. Pat. No. 4,021,240 discloses a combination of sulfonamidophenol-based reducing agents and four equivalent couplers.
In this process, an image of reduced silver and a color image are formed simultaneously in exposed areas by heat development and, therefore, the color image becomes cloudy or turbid. Although several processes have been proposed, including a process of removing the silver image by application of a liquid treatment and a process of transferring only the dye into another layer such as a sheet carrying an image-receiving layer, it is very difficult to distinguish between the unreacted material and dye and then to transfer the dye only.
Another process is described in Research Disclosure, May 1978, pages 54-58 (RD-16966) in which a nitrogen-containing heterocyclic ring is introduced in a dye, and a silver salt is formed and then the dye is released by heat development. In accordance with this process, however, it is difficult to control the release of dye in unexpected areas and thus a sharp image cannot be formed. Hence this process is not suitable for practical use.
Another process is to form positive color images by the heat-sensitive silver dye bleaching process. Useful dyes and bleaching techniques are described in, for example, Research Disclosure, April 1976, pages 30-32 (RD-14433), ibid., December 1976, pages 14-15 (RD-15227), and U.S. Pat. No. 4,235,957. This process, however, requires addition operation steps and materials in order to accelerate the bleaching of dye; for example, an activator sheet should be superposed and heated. Furthermore, this process has a disadvantage in that color images formed are gradually reduced and bleached by coexisting free silver, for example, during their long term storage.
Another process is to form color images utilizing leuco dyes, as described in, for example, U.S. Pat. Nos. 3,985,565 and 4,022,617. One of the defects of the process is that leuco dyes are difficult to stably incorporate in photographic material and thus the photographic material is gradually colored during the storage thereof.
The present invention is intended to overcome the above-described problems of the known light-sensitive materials, and provides a novel method for forming dye images by heating in a substantially water-free condition.